The present invention relates generally to intelligent electronic devices, e.g., electronic trip units, protective relays, energy meters and power quality meters. More specifically, the present invention relates to a method of detecting systemic event or fault conditions in an intelligent electronic device.
Intelligent electronic devices are well known. By way of example, an electronic trip unit (one such intelligent electronic device) typically comprises voltage and current sensors which provide analog signals indicative of the power line signals. The analog signals are converted by an A/D (analog/digital) converter to digital signals which are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. The ROM includes trip unit application code, e.g., main functionality firmware, including initializing parameters, and boot code. The EEPROM includes operational parameters for the application code.
The electronic trip unit detects fault conditions (i.e., events) such as breaker trips, relay events, downed conductors, or user defined event conditions. Once a fault condition is detected, the electronic trip unit generates an event message such as an alarm via a local display, external contacts, or by sending an event message to a centralized monitoring station such as a computer software program containing an event logging tool.
However, it is generally left to the user to analyze the raw event data to determine if the same event has occurred multiple times within a given time period such as to give indication that a systemic fault condition, i.e., a fault condition recurring due to the same root cause technical problem, exists which should be found and eliminated. There is especially a need in the area of utility relaying, where the physical environment surrounding the distribution systems often give rise to repeated faults which may be masked by automatic re-closure of breakers once the fault has cleared.
A method of detecting systemic fault conditions in an intelligent electronic device as indicated by repeated, similar fault events is presented. An electronic trip unit is described herein by way of example only, as the present invention applies to other intelligent electronic devices as well. In an exmplary embodiment of the invention the electronic trip unit comprises voltage and current sensors which provide analog signals indicative of the power line signals. The analog signals are converted by an A/D (analog/digital) converter to digital signals which are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which communicate with the microcontroller. The ROM includes trip unit application code, e.g., main functionality firmware, including initializing parameters, and boot code. The application code includes code for the systemic fault detection algorithm of the present invention. The EEPROM includes operational parameters, e.g., code for setting user defined events to be logged and/or time horizons for logging multiple similiar event occurrences, for the application code. These parameters may be stored in the trip unit at the factory and are selected to meet customer""s requirements, but. can also be remotely downloaded.
For each such event that is detected by the intelligent electronic device the systemic fault detection algorithm logs the occurrence of the event. Optionally, the algorithm may also log the date and time of the event. The algorithm determines if this particular fault type (or event type) has occurred before (e.g., the same type of fault on the same phase). If such a fault has occurred before, the time since the last such fault occurrence and the total number of such fault type occurrences are determined. This is then compared against the user-input number of events and/or time frequency specified to merit the generation of a repeat event.